1. Field of the Invention
The present invention relates to a new and improved method for making panels of composite wood material in a wet process wherein the outer face of the panel is deeply embossed and the back side of the panel is formed with a smoothly contoured surface generally following or matching the contour of the outer face rather than a conventional planar or flat back face. As a result of the new and unique process of the invention, the panels have excellent machining and paint absorption characteristics, and a much lower and more uniform moisture absorption rate than panels heretofore available. The panels have a lesser tendency to buckle or crack in the regions of relatively sharp relief on the outer face and are more stable in place after use and exposure in comparison to panels produced with molded or machined outer faces and a flat or planar back face.
2. Description of the Prior Art
In the past, panels of composite wood materials such as hardboard, fiberboard, flakeboard, chipboard, plywood and the like, having an embossed outer face with areas of deep relief therein, have a back side that is substantially planar or flat. This results in panels having wide variations in thickness at random positions over the surface area. In panels that were molded or formed under heat and pressure in a wet process from various types of wood composite materials, areas in the outer surface having deep relief or sharp angled intersections are often of high density and brittle structure resultng in premature cracking and excessive compression of the wood fibers. This resulted in uneven paint and moisture absorption characteristics, brittleness and cracking after exposure to and in general, pockets and/or streaks of materials of non-uniform density were present at various random locations on and below the outer surface of the panels. Moreover, when a deeply embossed outer face and a planar or flat back face is provided, there is a wide variety of thickness variations in the panels.
In the Greimer et al U.S. Pat. No. 4,061,813, a combination sheathing and support member is disclosed wherein contoured pressure molding dies are utilized to form a component of cellulosic particles and/or fibers with an adhesive binder in a single pressing operation.
In U.S. Pat. No. 4,188,762 a triple-lap harboard siding product is disclosed wherein relatively sharply angled intersecting surfaces on the outer face of the siding are formed in costly and time consuming machining operations. Such machining operations sometimes tend to leave exposed fiber ends on the outer surface of the siding member and such exposed fiber ends often cause excessive moisture absorption and swelling, as well as uneven paint or stain absorption.